The human brain is an extraordinarily complex and fine-tuned communications network containing billions of specialized cells (neurons) that give origin to our thoughts, emotions, perceptions and drives. Often, a drug is taken the first time by choice to feel pleasure or to relieve depression or stress.

Brain imaging research is revealing that the signals, or cues, that may spark an addicted person's desire to take drugs can be incredibly subtle or quick. Expanded knowledge about craving helps scientists develop new medical treatments for addiction.

Scientists have identified biology (including genes), mental health, social environment, childhood trauma and even the age at which a person begins to use drugs as key factors that affect whether or not a drug or alcohol user becomes addicted.

Most people who struggle with addiction will return to their drug or alcohol use (relapse) at least once. This is the result of the way the brain function has been altered by substance use. People differ in their susceptibility to relapse.

In May of 2006 HBO, USA Today and The Gallup Poll asked US adults, who have an immediate family member who has had a drug or alcohol addiction, a variety of question about addiction in general and the impact of addiction on their own lives.